Of the Nature of Movement
"If a wheel of which the movement has become very rapid continues to make many revolutions after its motive power has abandoned it, then this motive power continues to cause it to turn with the same quickness of movement, it would seem that this continuance necessitates but little force.
And I conclude that in order to maintain this movement only a slight effort by the motive power would be needed, and so much more as by nature it tends to become fixed."
MacCurdy, E. (1958). The Notebooks of Leonardo DaVinci. (pp 523). New York, NY: Braziller.